Hydrogen is highly desired as a secondary energy carrier and as a chemical raw material for many purposes. For example, it is desirable as a raw material for the production of synthetic resins, for the direct reduction of iron ore and for many other industrial and chemical manufacturing processes.
It has been found to be especially desirable to recover hydrogen from thermal energy which can be produced, for example, by a nuclear reactor. This has the advantage that a pure electrolysis of water need not be employed with its high consumption of electrical energy.
Processes for the generation of hydrogen are, of course, known using cyclical thermal processes. For example, U.S. Pat. No. 3,888,750 describes a process which is known as the sulfuric acid hybrid process. In this conventional process there are a number of process steps which require the supplying of thermal energy at high temperatures, for example for the vaporization of sulfuric acid and the thermal decomposition thereof to produce sulfur trioxide which can be further reacted to give sulfur dioxide and oxygen.
It is, of course, disadvantageous to use, as intermediates in the process, sulfur trioxide and sulfur dioxide since the latter have highly corrosive properties and are detrimental to the environment. Furthermore, the generation of oxygen by this technique requires especially high temperatures which create problems with respect to the materials from which the reactors are constituted.
In a publication entitled Development of Thermochemical Water Splitting for Hydrogen Production, at General Atomic Co., G.A-A, 14150, Sept. 30, 1976, page 20, Russell, McCorkle, J. H. Norman, J. R. Schuster, and P. W. Trester, describe a so--called sulfuric acid-iodine process in which apart from the vaporization of sulfuric acid and the splitting of sulfur trioxide, it is also necessary to decompose hydrogen iodide to produce the hydrogen. In this conventional process, the additional disadvantage arises that the use of hydrogen iodide requires special materials for the reactors in which the latter is handled.
U.S. Pat. No. 3,842,164 describes a process which utilizes the iron-chlorine system and in which compounds of iron, chlorine, oxygen and hydrogen, for example iron II and iron III oxides, iron II chloride, iron III chloride and hydrogen chloride are the reaction intermediates. In this process, oxygen also generated at extremely high temperatures and problems have been encounted in attempts to carry out the process on an industrial scale since several of the reaction intermediates are in the form of solids, thereby creating problems in the continuous feed and transport of the solids. Even intermittent or alternating feed of solids is a problem in this sense.
An additional disadvantage of the system of U.S. Pat. No. 3,842,164 is that several of the reaction intermediates are highly corrosive at high temperatures and produce or are compounds, e.g. chlorine, which are environmentally detrimental. Still another process for the generation of hydrogen has been described by R. G. Hickman, O. H. Krikorian and W. J. Ramsey in the Thermochemical Hydrogen Producetion Research at Lawrence Livermore Laboratory, The Hydrogen Economy, Miami Energy (THEME) Conference, 18-20 March 1974, Miami Beach, Fla., pages 11-23, 11-30 and 11-31 of the conference proceedings. This process is described as the methane-methanol-arsenic oxide process. In this process it is also disadvantageous that reaction intermediates are used which form as solids and are environmentally detrimental.
Apart from the processes described above, mention should also be made of the calcium-bromine-mercury process which is described in French Pat. No. 2,035,558. Even in this process the reaction intermediates include mercury and compounds thereof which are either solids and/or are detrimental to the environment if released thereto.
Naturally, a description of the processes known in the art for producing hydrogen and water by electrolysis in a practical manner would not be complete without mention of simple electrolysis. But this process, as has been noted, uses large quantities of electricity which may not be readily available in many instances, especially in the present state of world energy shortages.